Radiation Shielding Glossary

ALARA: The principle of radiation protection that calls for practical efforts to be taken to keep exposures to ionizing radiation "as low as reasonably achievable."

Alpha Particle: Alpha particles are the least penetrating and can be stopped by a thin layer of material, like a piece of paper. They do not pose a direct radiation threat; but pose a serious health threat if inhaled or ingested.

Becquerel (Bq): A unit, in the International System of Units (SI), used to measure radioactivity. One Becquerel is the amount of a radioactive material that will undergo one transformation in one second. Often, larger units like thousands (Kq), or millions (MBq) of Becquerels are used to measure radioactivity.

Beta Particle: Beta particles are more penetrating than alpha particles, but still can be absorbed by a thin sheet of aluminum. Beta particles can pose a serious direct radiation threat and can be lethal depending on the level. They also pose a serious health threat if inhaled or ingested.

Chronic Exposure: Exposure over a long time period, possibly resulting in adverse health effects.

Curie (Ci): The curie is the original unit used to measure radioactivity. It is based upon the radioactive decay rate of the radionuclide. One curie is equal to 37,000,000,000 transformations) per second. In the International System of Units, the becquerel (Bq) describes the amount of radioactive material present. One curie is equal to 3.7 x 10 9 Bq.

Electromagnetic Spectrum: The broad range of radiation types including radio waves; microwaves; infrared, visible, and ultraviolet light; and x and gamma rays.

Electron: Atomic particle with a negative electrical charge.

Exposure Rate: The amount of exposure per unit time (e.g., 1 mR/hour).

Gamma Ray: Gamma rays have high energy and a short wave length. They may cause an external or internal radiation hazard and are best shielded by thick layers of lead or steel. Gamma rays are similar to x-rays, but originate from the outer shell of the atom instead of the nucleus.

Geiger Counter: the portable device used to detect and measure radiation. When ionizing radiation passes through the Geiger Counter tube, a short, intense pulse of current passes from the negative electrode to the positive electrode and is counted. The number of pulses per second measures the radiation intensity.

Gray (Gy): From the International System of Units Gy is used to measure absorbed dose. One gray is equivalent to 100 rads. It relates to the amount of energy actually absorbed in any material, and is used for any type of radiation. Absorbed dose is usually expressed in terms of hundredths of a gray, or centi-grays.

Half-life: The amount of time it takes for half of the radioactivity in a substance to be gone or to decay. Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological half-life.

Neutrons: Neutrons are highly penetrating neutral (non-charged) particles, usually contained in the nucleus of an atom. Neutrons may be removed by processes like collision and fission

Neutron Doors: (also called Radiation Therapy Doors) Neutron doors are used to protect therapists and the public from repeated exposure during administration of radiation therapy. Neutron doors generally consist of 2 steel plates with a core of lead and polyethylene, reinforced with steel flat bars. Special radiation shielding frame systems are reinforced to prevent misalignment of hinges and are sometimes set in concrete to handle the weight of the doors. Neutron doors can be swinging or sliding doors and may or may not have automatic openers to prevent entrance during therapy.

Neutron Radiation: Energy released from an atom in the form of neutral particles (neutrons).

NRC: Nuclear Regulatory Commission independent regulatory agency created out of the Atomic Energy Commission in 1975 to regulate the civilian use of nuclear material.

Non-Ionizing Radiation: Non-ionizing radiation has a lower energy level and longer wavelengths than ionizing radiation. It is not strong enough to affect the structure of atoms, but can heat tissue and can cause harmful biological effects. Examples of non-ionizing radiation are radio waves, microwaves, and visible light.

Public Radiation Protection: Protection of the population as a whole from radiation.

Rad: The unit used to measure a quantity called absorbed dose. It is a measure of the energy absorbed per mass of material. One rad is equal to an absorbed dose of 0.01 J kg-1 (1 rad = 0.01 gray).

Radioactive Decay: The process wherein radionuclides lose radiation.. A number of different particles, including alpha and beta particles can be emitted by decay.

Radioactive Contamination: Deposition of radioactive material distributed over an area, equipment or person. It can be airborne, external or internal and tends to be unwanted, requiring cleaned up or decontamination.

Radioactive Material: material that contains radioactivity and emits ionizing radiation. It may be naturally occurring radioactivity from the environment or a material that was made radioactive.

Radioactivity: The transformation of an unstable atom that spontaneously releases energy in the form of photons (gamma rays for example) or subatomic particles (alpha particles for example).

Radiation Therapy Doors: (see Neutron Doors)

Radiation Weighting Factor: Factors developed for radiation protection and assessing health risks from radiation that take into account the biological effectiveness of different types of radiation.

Radiological: The general term concerning radiation and radioactive materials.

Radiological Protection: Radiological protection, sometimes known as radiation protection, is the science of protecting people and the environment from the harmful effects of ionizing radiation. It can be accomplished through the use of lead-lined and radiation shielding products.

Rem: Unit of measurement for equivalent does. Equivalent dose is often expressed in terms of thousandths of a rem, or mrem. The dose equivalent in rem is equal to the absorbed dose in rad multiplied by a quality factor that accounts for the biological effect of the radiation. (1 rem = 0.01 sievert).

Roentgen (R): The roentgen is a unit used to measure a quantity called exposure. This can only be used to describe an amount of gamma and X-rays in air.

Shielding: Material between a radiation source and an exposed person that reduces exposure, or shields radiation.

Sievert (Sv): A unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of millionths of a sievert, or micro-sievert. One sievert is equivalent to 100 rem.

X Ray: X rays are high energy radiation with no charge and short wave lengths. X rays can penetrate into the body and may cause an internal or external radiation hazard. Lead, steel or concrete shielding materials are often used to reduce the penetration of x rays.

X-Ray Glass:Leaded glass that allows technicians to view the imaging or radiation therapy procedure without exposure to radiation.

The information contained on our website, submittals, specifications, etc is offered for assistance in specifying products and materials from Radiation Protection Products, Inc. It is not intended to be complete and Radiation Protection Products, Inc. does not assume any responsibility for the adequacy of the submittals/specifications for a particular application. These submittals/specifications are subject to change without notice and without incurring obligation. Actual performance may vary in specific applications. An appropriate and qualified design professional/structural engineer must verify suitability of products for use in a particular application, as well as review final submittals/specifications. Radiation Protection Products, Inc.